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RESEARCH AND DESIGN OF AN IMPACT ABSORBING BARRIER FOR FIXED HIGHWAY OBJECTS

CONCEPTUAL STUDIES, ENGINEERING ANALYSIS AND DESIGN ARE SUMMARIZED FOR PROVIDING IMPACT ABSORBING BARRIERS AT FIXED ROADSIDE OBJECTS. THE OBJECTIVE OF THE RESEARCH IS TO IDENTIFY, ENGINEER, AND DESIGN PROTECTIVE BARRIERS FOR SUBSEQUENT ANALYTICAL EVALUATION AND FULL SCALE TESTING. SUCH BARRIERS ARE INTENDED TO REDUCE INJURIES AND PROPERTY DAMAGE RESULTING FROM UNAVOIDABLE COLLISIONS BETWEEN AUTOMOBILES AND FIXED OBJECTS NEAR THE ROADWAY. TWO BASIC BARRIER CONCEPTS OF A NUMBER INITIALLY PROPOSED WERE SELECTED BY THE BUREAU FOR ENGINEERING ANALYSIS AND DESIGN BY THE CONTRACTOR. THE FIRST BARRIER CONCEPT WAS THAT OF CONCENTRIC DUCTILE BEAMS FOR APPLICATION TO BRIDGE ABUTMENTS AND PIERS. THE SECOND BARRIER CONCEPT WAS THAT OF A LOW- STRENGTH, LIGHTWEIGHT MASONRY BARRIER FOR APPLICATION ON SIMILAR FIXED ROADSIDE OBJECTS. THE DUCTILE BEAM CONCEPT IS BASED ON THE PROGRESSIVE DEFLECTION AND YIELDING OF CONCENTRIC HORIZONTAL BEAMS SPACED AND ANCHORED AROUND THE FIXED OBJECT AT A TYPICAL VEHICLE CENTER-OF-GRAVITY HEIGHT. IMPACT REACTION FORCES FOR THE PLASTIC YIELDING OF THE ARCHED BEAM ARE PROVIDED BY TENSIONED STEEL CABLES BETWEEN THE OUTER BEAMS AND BETWEEN THE INNER BEAM AND THE FIXED OBJECT. THE DYNAMIC PERFORMANCE OF THE BARRIER HAS BEEN ANALYZED AND AN ENGINEERING DESIGN & DETAILED DRAWINGS HAVE BEEN PREPARED FOR EACH OF THE TWO APPLICATIONS. THE LOW- STRENGTH LIGHTWEIGHT MASONRY BARRIER CONCEPT IS BASED ON THE PROGRESSIVE COLLAPSING AND CRUMBLING OF A MINIMUM DENSITY MASONRY MATERIAL. THE BARRIER IS CONCEIVED TO ABSORB THE ENERGY OF THE COLLIDING VEHICLE BY THE CONTINUOUS CONTROLLED FAILURE OF THE MASONRY MATERIAL. A SIMPLIFIED ANALYSIS SUPPLEMENTED BY SOME ELEMENTARY MATERIAL TESTS INDICATES THAT LOW-DENSITY CONCRETE HAS SUITABLE DYNAMIC PHYSICAL PROPERTIES FOR IMPACT ABSORPTION. MORE COMPREHENSIVE STUDIES OF MATERIAL PROPERTIES AND FAILURE CRITERION ARE NEEDED BEFORE SPECIFIC DESIGNS FOR TEST AND EVALUATION ARE ATTEMPTED. TENTATIVE CONFIGURATIONS FOR MASONRY BARRIERS ARE SUGGESTED BASED ON THE LIMITED FINDINGS WHICH COULD BE MADE WITHIN THE SCOPE OF THIS STUDY. /AUTHOR/